Divider resistance



Sept. 3, 1940. oss 2,213,887

DIVIDER RES ISTANCE Filed April 23, 1938 lNVENTOR BY PAUL M. RossPatented Sept. 3, 1940 UNITED STATES PATENT OFFICE DIVIDER RE SISTANCEration of New Jersey Application April 23, 1938, Serial No. 203,357

6 Claims.

This invention relates to a potentiometer or divider resistance andparticularly to a resistance for use in connection with apparatus forrecordthe wave forms of high potential surges.

One cfoject of the invention is to provide a divider resistance in whichthe wave form of the voltage will be substantially the same at the lowpotential end of the resistance as at the high otential end; theresistance having means associated therewith for avoiding the effect ofcapacitance between portions of the resistance and earth.

A further object of the invention is to provide a potentiometer ordivider resistance which shall be of improved construction andoperation.

Other objects advantages will appear from the following description. Theinvention is eX- emplified by the combination and arrangement of partsshown in the accompanying drawing and described in the followingspecification, and it is more particularly pointed out in the appendedclaims.

In the drawing:

Fig. l. a diagrammatic representation of a ivider resistance madeaccording to the present in'ention and appl d to the oscillographcircuit of a high potential impulse generator.

Fig. 2 is a fragmentary sectional view of one unit of a dividerresistance made according to the present invention together with aportion of a connected unit, the figure also showing means forconnecting the two units.

Fig. 3 is an elevation of the circuit contacts connecting resistanceelements of adjacent units, the view being taken at right angles to Fig2.

Fig. i is an end view of one of the resistance units.

In the investigation of the characteristics of many high potentialelectrical devices, it is desirable to make a record of the Wave form ofhigh potential surges applied to these devices. The surges are usuallyproduced by some form of surge generator and apply in the manner described in Patent No. 2,077,773 granted April 20, 1937, to Harold L.Borden and myself, and assigned to The Ohio Brass Company of Mansfield,Ohio. I have discovered that in many oscillograph records, there is anappreciable variation between the wave form of the voltage impressed onthe test piece and the wave form recorded by the oscillograph due to thecapacitance currents to ground from the various portions of the dividerresistance interposed between the high potential electrode and theoscillograph.

In Fig. 1 of the drawing, the numeral H] designates the high potentialelectrode of a surge generator, which in operation is connected to oneterminal of the piece of electrical apparatus to be subjected to surgevoltages The electrode H9 is also connected to a non-inductive dividerresistance ll, the other end of which is connected through a cable 5 anda second non-inductive resistance it to ground. Spaced points on theresistance 53 are connected to the opposite surge deflecto plates iiiand 55 respectively, of the oscillograpa to impart a motion to thecathode ray of the oscillograph, corresponding to the Wave form of thevoltage impressed on the two plates. The operation or the impulsegenerator and the oscillograph are more fully described in the patentreferred to above.

I have discovered that the voltage at the point iii which is recorded bythe oscillograph may vary slightly in wave form from the voltage at thepoint and that this variation is due to the ca acitance to ground of thevarious portions the r sistance ii. By Onms law, the voltage between anytwo points in a circuit of pure resistance is equal to the currentflowing in the circuit times the resistance between the two oints andthis is independent of any time elebut this in its simple form, does not.ly to circuits containing capacitance. The ua on oi the variouscapacitance circuits bethe various points along the resistance H ground,contains a time factor, and a part he current flowing between theelectrode iii l round passes through these various capacitance circuits.The amount of current at any instance, passing through these shuntcircuits will vary as a factor of the time elapsed after the voltage .simpressed on the electrode. Since the current passing through theresistance conductor ii at the point 36 is in shunt with the current inthese various capacitance circuits, the current at this point dependupon a time factor due to the time factor of the capacitor shuntcircuits. The voltage atthe point it will, therefore, depend upon a timefactor and will not be a constant function or the voltage at the pointiii; hence, the wave form recorded by the oscillograph will not be atrue representation of the wave form on the electrode ii], due to theerror introduced by the time factor in the capacitance circuits betweenthe various portions of the resistance ii and ground.

To overcome this difficulty, I have surrounded the non-in activeresistance H with a second non-inductance resistance l1 connected toground through a resistance l8 which is equal to 55 the total resistancebetween the point l6 and ground. The resistance in the winding i1 isdistributed along the resistance of the winding ll proportionally to thedistribution of the resistance in the winding H, so that the drop ofpotential along the winding ll will be the same as the drop along thewinding l l and the voltage at any point along the winding 11 will bethe same as the voltage at the adjacent point along the winding i. Itwill be seen that the windin N forms a capacitance coupling with thewinding ll, but that the opposite points in this coupling are always ofequal potential, so that there is no tendency for capacitance current toflow between the two windings. This arrangement completely removes anycapacitance current between the winding ii and ground, so that with thenew arrangement, the pure non-inductive resistance l l constitutes theonly circuit between the points l9 and i5, and consequently, the voltageat the point it at any instant will be a direct factor of the voltage atthe point it, and the wave form recorded by the oscillograph will be anexact reproduction of the voltage wave form impressed on the electrodeHi. It is true that the capacitance between the winding ii and groundwill have a slight effect upon the voltage at the different points alongthe winding ll, but this variation of the voltage of winding ll from thevoltage at the adjacent-points of winding it will be so slight that thecapacitance current between the two windings caused thereby can bescarcely detected, and consequently, the eiiect upon the oscillographrecord will be negligible. This error can be still further reduced iffound desirable by adding other concentric resistance paths, each addedresistance reducing the error many fold. In practice, however, oneshielding resistance will usually be suflicient.

The divider resistance or potentiometer for a surge generator is usuallymade up in several units connected together in series and one form ofresistance element embodying the present invention is illustrated inFigs. 2, 3, and 4. In the embodiment shown there, each unit is providedwith a housing comprising a tube or shell i9 made of suitable rigiddielectric material. Metal caps 29 are secured to the opposite ends ofthe tube is by cap screws El engaging collars 22 cemented to the tube59. A second dielectric tube 23 is disposed inside the tube l9 and heldin place by shoulders 24% on the inner faces of the metal caps 2E3.Within the tube 23 there is a plurality of cards or plates of insulatingmaterial 25 each non-inductantly wound with a resistance wire 26, thecards and wires being connected by metal straps 217. The ends of thewires 26 of the endmost plates 25 are each connected to a contact member28. The contact members 23 extend through insulating bushings 29 in thecaps 2B of adjacent units, and the end of the contact member at one endof each of the units is provided with a spring clip 3i) which engages acontact clip 3i on the adjacent unit as shown more clearly in Figs. 2and 3. One end of each unit is provided with eyes 32 which engage hooks33 on the adjacent end of the adja cent unit. It will be seen that thevarious resistance units can be readily connected and disconnected toform a series of units of any desired length, and that when they areconnected, the windings 25 will be connected in series by the contactclips 363 and 3! to form the divider resistance.

Each of the dielectric tubes 23 is non-inductantly wound by a resistance34, the ends of the windings 3% being connected by conductor strips 35to the caps 20 at the ends of the tubes I9. It will be seen that thewinding 34 of each unit will have its opposite ends connected throughthe eyes 32 and hooks 33 with the adjacent ends of the correspondingwindings in the next adjacent units in the string. The windings 3d arethus all connected in series to form the winding ll of Fig. 1. To form acapacitance shield for the portion of the inner non-inductive circuitformed by the electrodes 28 and contact clips 3!] and 3|, conductingsleeve 35: connects the end caps of adjacent units and surrounds thecontacts between these units. This sleeve 36 may be of spring material,such as phosphor bronze, so as to make good electrical connection withthe adjacent end caps and assist the hook and eye connection inelectrically connecting the outer windings of adjacent units. The sleevemay be slit at one side as shown at 31 to provide sufiiient resiliencyto insure good electrical connection between the sleeve and end caps.The upper end of the sleeve is provided with an overhanging flange 38which supports the sleeve on the lower end cap of the upper unit. Whilethe units are being connected and disconnected, the sleeve is raised asshown in broken lines at the lower end of Fig. 2.

I claim:

.l. combination a non-inductive resistance ent arranged for theapplication of a voltage to one end of said element, and for conneconwith means for recording the voltage wave produced at the other end ofsaid element and means for shielding said resistance element from theefiects oi extraneous capacitance, said shielding means comprising asecond non-inductive resistance element surrounding said first namedelement and connected in parallel relation with said first namedelement, the impedance of said respective elements being so balancedthat adjacent points of said elements have substantially equalpotentials during the time said circuits are subject to said voltageWave.

In a potentiometer a non-inductive resistance and a shunt resistancehaving a portion thereof surrounding said first named resistance toreduce the effect, on the voltage distribution along said first namedresistance, of the capacitance between the portions of said first namedresistance and ground.

3. A divider resistance made up of a plurality of units, each unitcomprising a pair of nonindu-ctive resistance elements disposed onewithin the other, and means for connecting said units series, said meanscomprising contact members for electrically connecting the innermostelements of adjacent units together and the outermost elem nts or"adjacent units together.

4. A divider resistance comprising a plurality of units arranged to beconnected together in series, each unit comprising an inner core havinga resistance element non-inductantly wound thereon, a tubular membersurrounding said core and having a resistance element non-inductivelywound thereon and extending along and surrounding the conductor on saidcore, and contact members at the ends of each of said units adapted toengage complementary contact members on adjacent units and to connectelectrically the inner resistance elements and the outer resistanceelements, respectively, of adjacent units.

5. A divider resistance comprising a plurality of units connectedtogether in a string, each unit having inner and outer resistanceelements, contact members at the ends of said units connected With theends of said inner resistance elements, the contact members at adjacentends of adjacent units in a string being arranged to engage each otherto connect said inner elements in series, fittings for mechanicallyconnecting said units together in said string, the ends of the outerresistance elements in said units being connected to said fittingsrespectively, so that the outer resistance elements of adjacent units insaid string are electrically connected together by said fittings.

6. Means for reproducing, at a lower voltage, the wave form of a highvoltage impulse, said means comprising an elongated resistance member,said member being non-inductive so as to avoid distortion of the waveform by inductance,

and a second resistance member surrounding said first resistance memberand connected in parallel relation therewith and having the resistancethereof distributed proportionately to said first named resistance sothat equi-potential points in said resistances Will be in registrationwith one another, said second named resistance also being non-inductiveso that the equi-potential registration of said resistances will not bedisturbed by inductance for difierent wave forms of impressed voltage,said second resistance serving to shield said first resistance from theeffect of eX- traneous capacitance so that the voltage at spaced pointson said first resistance will not be influenced by either inductance orcapacitance and will reproduce the Wave form of the impressed voltage.

PAUL M. ROSS.

